There are many clinical situations in which it is desirable to have an accurate estimate of the pressure applied to a tissue of a body by a medical device or by a body part such as another tissue or organ. These clinical situations include: the evaluation of new and existing types of occlusive cuffs for pneumatic tourniquet systems and sphygmomanometers; the evaluation, improvement and standardization of the techniques employed by clinical staff in selecting and snugly applying an occlusive cuff to an extremity having a particular size, shape and tissue composition; the development and evaluation of innovative and potentially less expensive automatic tourniquet systems, including non-pneumatic tourniquet systems; the development and evaluation of advanced robotic devices and pre-robotic devices for tissue manipulation and limb manipulation in surgery and rehabilitation; the development and evaluation of improved, safer systems for a common anesthetic technique (intravenous regional anesthesia) which is based on the proper use of a special occlusive cuff; the development, improvement and evaluation of biomechanical models of tissue; the evaluation and fitting of special dressings and garments for applying pressure within a pressure-tolerance window to the tissue of burn patients in order to enhance healing; the diagnosis and treatment of compartmental pressure syndrome in orthopedics; the monitoring and control of sequential limb compression devices for prevention of deep venous thrombosis, and medical anti-shock trousers for emergency treatment; and perhaps the investigation and treatment of pressure sores in immobile patients.
Different types of biomedical pressure transducers known in the prior art may have a number of disadvantages when used in clinical situations such as those described above. First, many transducers known in the prior art are not sufficiently thin and flexible for interposing between selected body tissues and objects such as medical devices or body parts, e.g. organs, skeletal structures and other tissues, without displacing substantially either the tissue or the object. Transducers which require a rigid substrate for proper operation are not particularly useful for estimating the pressure applied to one soft tissue by an adjacent soft tissue, or for estimating the pressure applied to the tissue by an object having a curved or irregular surface. Many types of transducers known in the prior art are mass-produced in one standard form using expensive fabrication technologies to achieve economies of scale, and thus these transducers cannot be readily adapted. Adaption is important in many biomedical situations: it is frequently desirable to have a transducer array, or a plurality of transducers, for simultaneously estimating the pressures at a plurality of predetermined locations of a tissue beneath a pressure-applying object; and it is often desirable to change the number and area of the pressure transducers at those locations for selected combinations of tissues and objects. Similarly, in many prior art transducers which are mass-produced in one standard form, the composition and physical dimensions of various elements of these transducers cannot be conveniently and economically modified so that the transducer conforms more closely between a particular tissue and object of interest. Many of the biomedical pressure transducers known in the prior art are inherently complex and expensive, thus reducing the probability that such transducers might be conveniently and economically integrated if desired into medical devices such as occlusive cuffs, pressure dressings for burn patients, tissue retractors and the patient-applied parts of robotic systems for surgery and rehabilitation. Other transducers known in the prior art have the disadvantage that they cannot be conveniently sterilized by commonly used techniques, and this precludes the use of such prior-art transducers inside the body, either between adjacent soft tissues (e.g. in the diagnosis and treatment of compartmental pressure syndrome), or in surgery (e.g. between a soft tissue and an object such as a tissue retractor). Some transducers known in the prior art require complex and expensive support circuitry, and others require difficult and time-consuming calibration procedures. Another disadvantage of some prior-art transducers is that their accuracy and hysteresis cannot be conveniently checked by clinical staff in a health-care environment using readily available apparatus and electronic pressure transducers. A final disadvantage of certain biomedical pressure transducers is that, because of unacceptable inaccuracy, calibration difficulties or unreliability associated with repetitive usage, these transducers cannot be safely incorporated into systems for automatically controlling the pressure applied to a body tissue near a predetermined location.
The biomedical pressure transducer of the present invention was developed to overcome many of the disadvantages of prior-art transducers for clinical situations such as those indicated above. The transducer of the present invention makes advantageous use of some of the technology developed for, and now commonly employed in, the fabrication of inexpensive and flexible membrane switches in small batches for a wide variety of applications.
The applicant is aware of the following United States patents which are more or less relevant to the subject matter of the applicant's invention.
______________________________________ 4,605,010 8/1986 McEwen 128/686 4,479,494 10/1984 McEwen 128/327 128/682 4,469,099 9/1984 McEwen 128/327 128/682 4,300,029 11/1981 Maser 200/159B 4,218,600 8/1980 Kissner 200/159B 4,217,473 8/1980 Parkinson 200/159B 3,095,873 7/1963 Edmunds 128-2.05 ______________________________________
The following U.S. patent applications of the applicant are more or less relevant to the subject matter of the applicant's invention.
U.S. application Ser. No. 921,461; Title-Occlusive Cuff; Art Unit-335; Inventor-McEwen.
U.S. continuation-in-part-application Ser. No. 831,001; Title-Advanced Medical Robot; Art Unit 335; Inventors: McEwen et al.
U.S. application Ser. No. 006,131; Title-Patient Limb Positioning Apparatus; Art Unit-N/A; Inventors: Auchinleck, McEwen et al.
The applicant is also aware of the following published references which are more or less relevant to the subject matter of the applicant's invention.
J. A. McEwen and R. W. McGraw, "An adaptive tourniquet for improved safety in surgery." IEEE Transactions in Biomedical Engineering, Vol.BME-29, February 1982, pp. 122-128.
J. A. McEwen and G. F. Auchinleck, "Advances in surgical tourniquets." J. Assn. Operating Room Nurses, Vol. 36, 1982, pp. 889-896.
J. A. Shaw and D. G. Murray, "The relationship between tourniquet pressure and underlying soft-tissue pressure in the thigh." The Journal of Bone and Joint Surgery, Vol. 64-A, 1982, pp. 1148-1152.
A. C. McLaren and C. H. Rorabeck, "The pressure distribution under tourniquets." The Journal of Bone and Joint Surgery, Vol. 67-A, 1985, pp. 433-438.
R. J. Newman and A. Muirhead, "A safe and effective low pressure tourniquet." Journal of Bone and Joint Surgery, Vol. 68-B, 1986, pp. 625-628.
J. A. Shaw, W. W. Demuth, an A. W. Gillespy, "Guidelines for the use of digital tourniquets based on physiological pressure measurements." The Journal of Bone and Joint Surgery, Vol. 67-A, 1985, pp. 1086-1090.
S. E. Grice et al., "Intravenous regional anesthesia Evaluation and prevention of leakage under the tourniquet." Anesthesiology, Vol. 65, pp. 316-320, 1986.